linux-kernel - Re: Duplicate fields in event format of `regcache

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Date:   Fri, 20 Nov 2020 13:47:46 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Philippe Duplessis-Guindon <pduplessis@...icios.com>
Cc:     linux-trace-devel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>,
        Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: Duplicate fields in event format of `regcache_sync `

On Fri, 20 Nov 2020 12:50:33 -0500
Philippe Duplessis-Guindon <pduplessis@...icios.com> wrote:

> Hi,
> 
> I am doing an ftrace plugin for Babeltrace 2 [1], and while I was 
> parsing the event fields I had an error saying that `regcache_sync` has 
> 2 fields named `type`. The problem seems to come from the 
> drivers/base/regmap/trace.h file [2]. This is the patch where this was 
> added: [3]. The `int field` type is not assigned, so I was wondering if 
> it is normal that the field is there.
> 
> This is the format of this event:
> 
> $ sudo cat /sys/kernel/debug/tracing/events/regmap/regcache_sync/format
> name: regcache_sync
> ID: 1216
> format:
>    field:unsigned short common_type;    offset:0;    size:2;    signed:0;
>    field:unsigned char common_flags;    offset:2;    size:1;    signed:0;
>    field:unsigned char common_preempt_count; offset:3; size:1;signed:0;
>    field:int common_pid;    offset:4;    size:4;    signed:1;
> 
>    field:__data_loc char[] name;    offset:8;    size:4;    signed:1;
>    field:__data_loc char[] status;    offset:12;    size:4;    signed:1;
>    field:__data_loc char[] type;    offset:16;    size:4;    signed:1;
>    field:int type;    offset:20;    size:4;    signed:1;
> 
>    print fmt: "%s type=%s status=%s", __get_str(name), __get_str(type), 
> __get_str(status)
> 

It looks like dumb luck that this ever worked. :-/

The correct fix is to nuke that "int type" field. It's not even assigned.

Thanks for pointing this out.

-- Steve


> Thank you,
> 
> Philippe
> 
> 
> [1] https://babeltrace.org/
> 
> [2] 
> https://github.com/torvalds/linux/blob/master/drivers/base/regmap/trace.h#L129
> 
> [3] 
> https://github.com/torvalds/linux/commit/593600890110c02eb471cf844649dee213870416